The present invention relates to a method for the low temperature cleaning of the atmosphere and more particularly to the rendering of the outer surface of a substrate, such as a radiator of a motor vehicle, capable of either catalytically converting atmospheric pollutants to less harmful materials or adsorbing such pollutants without adversely affecting the functioning of the substrate. The method is accomplished through the employment of a pollutant treatment coating on the surface of such substrate said coating being further provided with an overcoating of either a protective material alone or in combination with a water repellant material which improves durability and long term performance of the catalytic or adsorptive coating.
A review of literature relating to pollution control reveals that the general approach is to reactively clean waste streams entering the environment. If too much of one pollutant or another is detected or being discharged, the tendency has been to focus on the source of the pollutant. For the most part gaseous streams are treated to reduce the pollutants prior to entering the atmosphere.
It has been disclosed to treat atmospheric air directed into a confined space to remove undesirable components therein. However, there has been little effort to treat pollutants which are already in the environment; the environment has been left to its own self-cleansing systems.
References are known which disclose proactively cleaning the environment. U.S. Pat. No. 3,738,088 discloses an air filtering assembly for cleaning pollution from the ambient air by utilizing a vehicle as a mobile cleaning device A variety of elements are disclosed to be used in combination with a vehicle to clean the ambient air as the vehicle is driven through the environment. In particular, there is disclosed ducting to control air stream velocity and direct the air to various filter means. The filter means can include filters and electronic precipitators. Catalyzed postfilters are disclosed to be useful to treat non-particulate or aerosol pollution such as carbon monoxide, unburned hydrocarbons, nitrous oxide and/or sulfur oxides, and the like.
Another approach is disclosed in U.S. Pat. No. 5,147,429. There is disclosed a mobile airborne air cleaning station. In particular this patent features a dirigible for collecting air. The dirigible has a plurality of different types of air cleaning devices contained therein. The air cleaning devices disclosed include wet scrubbers, filtration machines, and cyclonic spray scrubbers.
The difficulty with devices disclosed to proactively clean the atmospheric air is that they require new and additional equipment. Even the modified vehicle disclosed in U.S. Pat. No. 3,738,088 requires ducting and filters which can include catalytic filters.
DE 40 07 965 C2 to Klaus Hager discloses a catalyst comprising copper oxides for converting ozone and a mixture of copper oxides and manganese oxides for converting carbon monoxide. The catalyst can be applied as a coating to a self-heating radiator, oil coolers or charged-air coolers. The catalyst coating comprises heat resistant binders which are also gas permeable. It is indicated that the copper oxides and manganese oxides are widely used in gas mask filters and have the disadvantage of being poisoned by water vapor. However, the heating of the surfaces of the automobile during operation evaporates the water. In this way, continuous use of the catalyst is possible since no drying agent is necessary.
Responsive to the difficulties associated with devices which proactively treat the atmosphere, the Assignee herein in U.S. patent application Ser. No. 08/410,445 filed on Mar. 24, 1995, now abandoned, U.S. patent application Ser. No. 08/589,182 filed Jan. 19, 1996, now abandoned, and U.S. patent application Ser. No. 08/589,030 filed Jan. 19, 1996, now U.S. Pat. No. 6,200,542 B1 issued Mar. 13, 2001, each incorporated herein by reference, disclosed apparatus in related methods for treating the atmosphere by employing a moving vehicle. In preferred embodiments, a portion of the surface of the engine or cabin cooling system (e.g., the radiator, air conditioning condenser, etc.) is coated with a catalytic or adsorptive composition. Additionally, the fan associated with the engine cooling system can operate to draw or force air into operative contact with the radiator. Pollutants contained within the air such as ozone, hydrocarbons and/or carbon monoxide are then catalytically convened to non-polluting compounds (e.g., oxygen, water and carbon dioxide).
The Assignee herein also has pending U.S. patent application Ser. No. 08/412,525 filed on Mar. 29, 1995, now abandoned, incorporated herein by reference, which discloses devices and methods for proactively treating the atmosphere catalytically by employing a stationary object such as selected surfaces of an automobile at rest, a billboard, an air conditioning unit and the like coated with a catalytic composition.
In addition, International Publication No. WO 98/02235 of the Assignee herein discloses a process of catalytically activating the surface of a heat exchange device such as a motor vehicle radiator while retaining the heat exchange properties of the device. The method enables the catalytic treatment of the atmosphere by converting pollutants contained therein to less harmful materials while allowing the radiator to perform its function normally. A polymeric protective coating which is stable up to temperatures of about 100xc2x0 C. may be employed to retard degradation and inactivation of the catalyst.
The application of a catalyst or absorbent composition to the surface of a substrate such as a radiator of a motor vehicle presents problems such as the exposure of the composition to relatively high concentrations of contaminants which can deleteriously affect the functioning of the composition. Such contaminants include solid or vaporized particulates, corrosive compounds such as salts and oxides of nitrogen, sulfur and the like. Contact of the composition with such contaminants can result in masking, fouling and/or poisoning. In addition, water (and contaminants contained therein) can be a source of degradation and can also decrease the activity and useful life of catalyst and adsorbent compositions.
It would therefore be a significant advance in the art of reducing atmospheric pollution to employ catalytic and adsorptive composition coated devices for the treatment of the atmosphere to remove pollutants contained therein wherein the composition is protected against those contaminants commonly encountered in the atmosphere which can adversely affect performance of the composition. It would be a further advance in the art if the composition could be protected from contaminants at from ambient temperatures up to about several hundred degrees centigrade. It would be still a further advance in the art if the composition could be protected from water especially liquid water.
The present invention generally relates to a method and device for cleaning the atmosphere by removing pollutants therefrom. A surface which contacts the atmosphere such as a surface of a radiator of a motor vehicle is treated with a catalyst or absorbent composition so that the outer surface (i.e., air side) thereof is capable of either adsorbing pollutants or catalytically converting pollutants contained in the atmosphere into less harmful substances. The composition is coated at least in part (preferably completely) with a porous, protective coating as defined herein which effectively protects the composition from atmospheric contaminants at ambient temperatures up to several hundred degrees centigrade or higher. Preferably, the porous protective coating is itself overcoated with a hydrophobic material. The present invention also encompasses devices treated in the manner described herein.
The term xe2x80x9cadsorptionxe2x80x9d is defined as including: (a) the penetration of one substance into the inner structure of another (commonly referred to as xe2x80x9cabsorptionxe2x80x9d); and (b) adherence of the atoms, ions, or molecules of a gas or liquid to the surface of another substance (commonly referred to as xe2x80x9cadsorptionxe2x80x9d). See, for example, Hawley""s Condensed Chemical Dictionary, Thirteenth Edition, Van Nostrand Reinhold, 1997, pp. 2, 3, 24.
Similarly, related terms such as, for example, adsorbents, adsorbing, adsorptive, etc. shall be understood to include both related meanings. The term xe2x80x9catmospherexe2x80x9d means the mass of air surrounding the earth, and includes xe2x80x9cambient airxe2x80x9d which is the portion of the atmosphere that is drawn or forced towards the outer surface of the coated substrate. Ambient air includes air, which has been heated either incidentally or by a heating means. The term xe2x80x9csubstratexe2x80x9d is used in its customary broad sense and includes any surface which can be coated with a suitable catalyst or adsorbing composition and thereafter have the composition protected in the manner described herein. Such surfaces include those surfaces found in motor vehicles such as automobiles, trucks, vans, buses, trains, airplanes and the like and include but are not limited to radiators, condensers, charge air coolers, transmission coolers, inserted devices which may be separately heated, heat exchangers, fluid transporting conduits and the like. Surfaces normally described as stationary such as billboards, road signs, outdoor HVAC equipment are also included. For convenience only, a motor vehicle radiator will be discussed herein as typical of a suitable substrate.
In accordance with the present invention, the surface of the substrate (e.g., radiator) is provided with a substance which can either effectively catalyze the conversion of pollutants contained in the atmosphere to less harmful substances or adsorb such pollutants for later treatment as appropriate. The surface of the radiator is therefore capable of either catalytically converting pollutants such as hydrocarbons, carbon monoxide and ozone into less harmful materials such as oxygen, carbon dioxide and water, or adsorbing pollutants such as NOx, SOx hydrocarbons and carbon monoxide as the case may be.
In one aspect, the present invention is directed to a method of catalytically treating the atmosphere to convert pollutants to less harmful materials comprising treating an outer surface of a substrate, particularly an auto radiator to render said surface capable of catalytically converting said pollutants and then providing the catalyst with an overcoating of at least one material or mixtures of such materials which is porous and preferably also adsorbent (hereinafter, xe2x80x9cporous protective materialxe2x80x9d). The porous protective material is preferably sufficiently porous to enable the atmosphere including the contained pollutants to be treated to pass therethrough into operative contact with the catalyst composition to enable conversion thereof into less harmful materials. The porous protective material preferably should also be adsorbent in order to trap atmospheric catalyst degradating contaminants so that they are at least substantially prevented from reaching the catalyst composition. Still further, the catalyst and the porous protective material are preferably stable at ambient temperatures and up to about several hundred degrees centigrade.
In another aspect of the invention, the porous protective material may include or be overcoated with at least one substance which is capable of protecting the catalyst composition from contact with liquid water and/or water vapor (hereinafter, xe2x80x9chydrophobic protective materialxe2x80x9d).
In another aspect of the invention, the outer surface of the substrate (e.g. radiator) is made of or provided with a catalytically active substance such as a base metal catalyst (e.g. manganese dioxide), precious metal catalyst or combination thereof. As used herein the terms xe2x80x9cbase metal catalystxe2x80x9d and xe2x80x9cprecious metal catalystxe2x80x9d shall include the base metals and precious metals themselves as well as compounds containing the same e.g., salts and oxides and the like.
In another aspect, the present invention is directed to a method for cleaning the atmosphere comprising treating an outer surface of a substrate, particularly an auto radiator with an adsorptive material to render said surface capable of adsorbing pollutants present in the atmosphere such as NOx, SOx hydrocarbons and carbon monoxide and then providing the adsorptive material with an overcoating of at least one porous protective material.
In another aspect of the invention, the outer substrate surface coated with either a catalyst composition or adsorbing composition, is coated with the porous protective material which is then overcoated with a hydrophobic protective material. The protective material, whether porous, hydrophobic or a combination of both still permits pollutants to pass into contact with either the catalyst composition so they may be converted to less harmful materials or into contact with the adsorbing composition so that they may be absorbed and thereby removed from the atmosphere.
The coatings contemplated for use herein do not substantially interfere with the normal desired operation of the substrate (e.g., auto radiator) whose surface has been coated.